Most refrigeration systems are not 100% free of leaks. Thus, the amount (or mass) of refrigerant within the refrigeration system decreases over time. Refrigeration systems, however, are designed to operate with a specific amount of refrigerant. Therefore, loss of refrigerant in a refrigeration system over time typically reduces the efficiency of the refrigeration system. Also, if the amount of refrigerant in the refrigeration system drops to a certain level, the refrigeration system may cease to operate and/or be damaged. For these reasons, a common maintenance operation for a refrigeration system is to recharge the refrigerant within the refrigeration system.
The recharging operation typically involves evacuating the refrigeration system of any remaining refrigerant and, if present, other materials within the refrigeration system. Once the refrigeration system is evacuated, a predetermined amount of new refrigerant is introduced into the refrigeration system. An important component of conventional refrigeration charging systems is the device that measures the amount of refrigerant introduced into the refrigeration system. Since the refrigeration system is designed to operate with a specific amount of refrigerant, too little or too much refrigerant can reduce the effectiveness of the refrigeration system.
One conventional device used to measure the amount of refrigerant introduced into the refrigeration system is a load cell (or scale). Essentially, the load cell measures the weight of a tank containing the refrigerant before the refrigerant is introduced into the refrigeration system and then afterwards. The difference between the two readings is the amount of refrigerant introduced into the refrigeration system. There are, however, certain problems that are associated with the use of a load cell in conventional charging systems. Load cells are sensitive to vibration, which can throw off the measurements. Also, since the load cell determines the weight of the entire tank used to supply the refrigerant, when the weight of the tank is increased, the sensitivity of the load cell is reduced.
Furthermore, recent advances in refrigeration technology employ carbon dioxide as the refrigerant, which is stored at a pressure as much as ten times higher than the pressure at which conventional refrigerants are stored, and the resulting increase in storage pressure necessitates thicker walls for the tank. These thicker walls add additional weight to the tank, which further decreases the sensitivity of the load cell.
As those skilled in the art appreciate, the manufacturers specifications are generally accurate, but provide ranges of acceptable charge to account for variances, even between identical vehicle models. Some manufacturers, such as Mercedes-Benz, Volvo, Saab and Fiat publish single or exact numbers for the required charge (e.g., 800 grams). Other manufacturers, such as BMW, Ford, VW and Peugeot, provide a target number with a tolerance range (e.g., 750 grams +/−50 grams). Yet other manufacturers, such as many Japanese manufacturers, specify an overall range (e.g., 500-600 grams), and this variation can lead to confusion. There is, therefore, a need for a refrigerant charging system and method that is more accurate and vibration-resistant, and by which technicians may independently assess an optimal refrigerant charge for the refrigeration system.